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RESEARCH AND PRACTICE |
The authors are with the Department of Epidemiology, Mailman School of Public Health, Columbia University, New York City. Habibul Ahsan is also with the Herbert Irving Comprehensive Cancer Center, Columbia University.
Correspondence: Requests for reprints should be sent to Habibul Ahsan, MD, MMedSc, Department of Epidemiology, 722 W 168th St, Room 720G, Mailman School of Public Health, Columbia University, New York, NY 10032 (e-mail: habibul.ahsan{at}columbia.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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We assessed the potential burden of internal cancers due to arsenic exposure in Bangladesh. We estimated excess lifetime risks of death from liver, bladder, and lung cancers using an exposure distribution, death probabilities, and cancer mortality rates from Bangladesh and dose-specific relative risk estimates from Taiwan. Results indicated at least a doubling of lifetime mortality risk from liver, bladder, and lung cancers (229.6 vs 103.5 per 100 000 population) in Bangladesh owing to arsenic in drinking water.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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The principal cause of arsenic-induced mortality is cancer,6–10 but little is known regarding future cancer mortality risks attributable to arsenic exposure among the population of Bangladesh.1 The goal of the present study was to estimate excess lifetime mortality rates for the most-established arsenic-related internal cancers (i.e., lung, liver, and bladder cancers)7–10 in Bangladesh.
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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The arsenic exposure distribution in Bangladesh was ascertained from a sample of 65 876 people who represented the source population of an ongoing prospective cohort study focusing on the health effects of exposure to arsenic in drinking water. Water samples from 5966 contiguous hand-pumped tube wells in a well-defined geographic area of Araihazar, Bangladesh, were collected and tested for arsenic in 2000. Well owners were interviewed to collect data on the numbers and characteristics of the 65 876 regular users.11
Gender-specific lifetime mortality risks from liver, bladder, and lung cancers among the population of Bangladesh were derived, via life table methods, from the formula 
S(tk)Pk. Values of S(tk) indicate the probability of surviving to the beginning of each of the 5 (i.e., k = 1–5) age groups assessed (0–14, 15–44, 45–54, 55–64, 
65 years). Survival estimates were based on gender- and age-specific death probabilities among the overall population of Bangladesh.12 Values of Pk indicate gender-, age-, and cancer-specific mortality rates in Bangladesh; these rates were computed by the International Agency for Research on Cancer (IARC).13–16
Gender-specific, age-adjusted relative risks of liver, bladder, and lung cancer mortality due to arsenic exposure were computed on the basis of gender- and age-specific data on arsenic exposure, cancer mortality, and at-risk population obtained from studies conducted in Taiwan (detailed data regarding a published study17 were obtained from C. J. Chen and L. Ryan, January 2002). We used Poisson regression models in calculating these risk estimates, allowing us to compare rates for different levels of arsenic exposure in an endemic area with those in the general population of Taiwan.
Finally, we estimated lifetime excess mortality risks attributable to different levels of arsenic exposure by multiplying gender-specific, age-adjusted excess relative risks from Taiwan by the corresponding category-specific lifetime risks for each cancer in Bangladesh. We weighted these estimates by the arsenic exposure distribution ascertained from our study population in Bangladesh to derive overall lifetime excess risk estimates.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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).
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). Overall lifetime excess mortality risks (per 100 000) from the 3 cancers in combination were 198.3 for males and 53.8 for females, with an average across-gender lifetime risk of 126.1.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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Several uncertainties involved with our estimations warrant caution in interpreting our findings. First, in generating our exposure distribution, we were unable to pool data from other large-scale surveys conducted in Bangladesh since water samples in those surveys were not collected in a systematic manner and the population distributions of the individual exposure categories were unknown. However, the extent of arsenic contamination in our study area was comparable to estimates reported in those large-scale surveys.2,5,19
Second, the dose-specific relative risk estimates we used in predicting risks were derived from Taiwan data, since no such estimates are currently available in Bangladesh. Data from Taiwan have also been used in most arsenic risk assessments for the US population.18,20–22 Given the long latency of arsenic-induced cancer and the similarity in durations of well water use between the exposed populations of Taiwan (1910s–1970s)7 and Bangladesh (since the 1940s),19 the effects of arsenic are assumed to be similar in the 2 populations.
Although our relative risk estimates did not demonstrate a strict dose–response pattern, lifetime excess risk estimates did not change appreciably when the exposure categories were grouped differently (data not shown). However, the impact of potential differences in the distributions of other risk factors related to the studied cancers between the populations of Bangladesh and Taiwan is unknown. The prevalence of cigarette smoking among Bangladeshi men (56–72%) is higher than the prevalence reported in the Taiwan study from which we generated the present relative risk estimates (32%), and nutritional deficiency is more prevalent in Bangladesh.23–25 Hepatitis B virus infection was probably more prevalent in Taiwan in the 1980s, the period during which the relative risk estimates used in the present study were derived.26,27 Whether the 2 populations are comparable in terms of arsenicrelated genetic factors is unknown.
Finally, the IARC estimated cancer mortality rates for Bangladesh on the basis of cancer incidence rates in India, age-specific cancer ratios in Bangladesh, and cancer survival rates in developing countries.13–16 Because cancer mortality data are scant in Bangladesh, it is difficult to evaluate the validity of the IARC estimates. However, given the geographic and sociocultural similarities of India and Bangladesh, and the dissimilarity of the 2 countries in regard to arsenic exposure, the IARC estimates are probably the best data available for estimating "background" lifetime risks.
In conclusion, our results suggest at least a doubling of the potential cancer burden in Bangladesh due to arsenic exposure. Measures focusing on reductions in arsenic exposure, early diagnosis, and treatment of arsenic-induced cancers are thus urgently warranted. In addition, risk estimates derived directly from individual-level data are needed for more precise risk assessments tailored to the population of Bangladesh. Prospective analyses based on our ongoing epidemiological cohort study will address this issue in the near future.
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Acknowledgments |
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We acknowledge Faruque Parvez, Joseph Graziano, Alexander van Geen, and Iftikhar Hussain for their contribution in generating the data that provided the basis for our estimation of the arsenic exposure distribution in Bangladesh. We also acknowledge the generosity of Chien-Jen Chen of the National Taiwan University, who provided us with the original data on cancer mortality rates and arsenic exposures in Taiwan, and Jacques Ferlay of IARC, who provided detailed insights regarding IARC data.
Human Participant Protection
No protocol approval was needed for this study.
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Footnotes |
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Accepted for publication May 6, 2003.
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References |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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2. Chowdhury UK, Biswas BK, Chowdhury TR, et al. Groundwater arsenic contamination in Bangladesh and West Bengal, India. Environ Health Perspect. 2000;108:393–397.[ISI][Medline]
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5. British Geological Survey. The groundwater arsenic problem in Bangladesh (phase 2). Available at: http://www.bgs.ac.uk/arsenic. Accessed January 10, 2003.
6. Chen CJ, Kuo TL, Wu MM. Arsenic and cancers. Lancet. 1988;1:414–415.
7. Chen CJ, Chen CW, Wu MM, Kuo TL. Cancer potential in liver, lung, bladder and kidney due to ingested inorganic arsenic in drinking water. Br J Cancer. 1992;66:888–892.[ISI][Medline]
8. Smith AH, Goycolea M, Haque R, Biggs ML. Marked increase in bladder and lung cancer mortality in a region of northern Chile due to arsenic in drinking water. Am J Epidemiol. 1998;147:660–669.
9. Hopenhayn-Rich C, Biggs ML, Fuchs A, et al. Bladder cancer mortality associated with arsenic in drinking water in Argentina. Epidemiology. 1996;7:117–124.[ISI][Medline]
10. Hopenhayn-Rich C, Biggs ML, Smith AH. Lung and kidney cancer mortality associated with arsenic in drinking water in Cordoba, Argentina. Int J Epidemiol. 1998;27:561–569.
11. van Geen A, Ahsan H, Horneman AH, et al. Promotion of well-switching to mitigate the current arsenic crisis in Bangladesh. Bull World Health Organ. 2002;80:732–737.[ISI][Medline]
12. Statistical Yearbook of Bangladesh. Dacca, Bangladesh: Bangladesh Bureau of Statistics; 1999.
13. Ferlay J, Bray F, Pisani P, Parkin DM. GLOBOCAN 2000: Cancer Incidence, Mortality and Prevalence Worldwide, Version 1.0. Lyon, France: International Agency for Research on Cancer; 2001. IARC cancer base 5.
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15. Bangladesh Cancer Epidemiology Research Programme, 1976–1981. In: Parkin DM, ed. Cancer Occurrence in Developing Countries. Lyon, France: International Agency for Research on Cancer; 1986:195–198.
16. Sankaranarayanan R, Black RJ, Parkin DM. Cancer Survival in Developing Countries. Lyon, France: International Agency for Research on Cancer; 1998. IARC scientific publication 145.
17. Morales KH, Ryan L, Kuo TL, Wu MM, Chen CJ. Risk of internal cancers from arsenic in drinking water. Environ Health Perspect. 2000;108:655–661.[ISI][Medline]
18. Smith AH, Hopenhayn-Rich C, Bates MN, et al. Cancer risks from arsenic in drinking water. Environ Health Perspect. 1992;97:259–267.[ISI][Medline]
19. United Nations Children’s Fund. Arsenic mitigation in Bangladesh. Available at: http://www.unicef.org/arsenic/. Accessed January 10, 2003.
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21. National Research Council, Subcommittee on Arsenic in Drinking Water. Statistical Issues: Arsenic in Drinking Water. Washington, DC: National Academy Press; 1999:264–299.
22. Bates MN, Smith AH, Hopenhayn-Rich C. Arsenic ingestion and internal cancers: a review. Am J Epidemiol. 1992;135:462–476.
23. Ke-You G, Da Wei F. The magnitude and trends of under- and over-nutrition in Asian countries. Biomed Environ Sci. 2001;14:53–60.[ISI][Medline]
24. Efroymson D, Ahmed S, Townsend J, et al. Hungry for tobacco: an analysis of the economic impact of tobacco consumption on the poor in Bangladesh. Tob Control. 2001;10:212–217.
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26. Rahman M, Amanullah, Sattar H, Rahman M, Rashid HA, Mollah AS. Sero-epidemiological study of hepatitis B virus infection in a village. Bangladesh Med Res Counc Bull. 1997;23:38–41.[Medline]
27. Beasley RP, Hwang LY, Lin CC, Chien CS. Hepatocellular carcinoma and hepatitis B virus: a prospective study of 22 707 men in Taiwan. Lancet. 1981;2:1129–1133.[ISI][Medline]
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